Field of the Invention
The present invention relates to an air bag of an air bag system mounted on a vehicle for protecting an occupant at the time of a vehicular collision.
Description of the Related Art
An air bag system mounted for a driver's seat or in an instrument panel is constructed to have its air bag extended quickly with the gas injected from an inflator (or gas generator) when the vehicle collides.
This air bag is made of cloth and is formed at its rear end with an opening for receiving the inflator and at its rear face with vent holes. The air bag is sewed by threads with reinforcing cloth patches at the peripheral edges of those opening and vent holes.
When the extended air bag is hit by the human body, it releases the internal gas through the vent holes to the outside to damp the shock to the body.
When the inflator is activated to inject the gas, the threads sewing the reinforcing cloth patches are exposed to a high temperature because the gas is considerably hot. This makes it necessary for the threads to be made of heat-resisting materials such as aramid fibers (i.e., aromatic polyamide fibers) so that the cost is accordingly raised. On the other hand, most of the heat-resisting fibers are thick to stiffen the portions reinforced with the cloth patches, thus raising another problem of making the air bag hard to fold.
Alternatively, the threads are made heat-resistant by coating them with silicone resin or rubber. This method also causes the problems of high cost and difficulty in folding the air bag.